1. Field of the Invention
The present invention relates generally to polymeric well completion and remedial compositions which form highly pliable impermeable masses having desired properties and methods of using such compositions.
2. Description of the Prior Art
Hydraulic cement compositions have heretofore been utilized in subterranean well completion and remedial operations. For example, hydraulic cement compositions have been used in primary cementing operations whereby casings and liners are cemented in well bores. In performing primary cementing, a hydraulic cement composition is pumped into the annular space between the walls of a well bore and the exterior surfaces of a casing string or liner disposed therein. The cement composition is permitted to set in the annular space thereby forming an annular sheath of hardened substantially impermeable cement therein. The cement sheath physically supports and positions the casing or liner in the well bore and bonds the exterior surfaces of the casing or liner to the walls of the well bore whereby the undesirable migration of fluids between zones or formations penetrated by the well bore is prevented.
Set cement in wells, and particularly the rigid set cement in the annuluses between casing and liners and the walls of well bores, often fail due to shear and compressional stresses exerted on the set cement. Such stress conditions are typically the result of relatively high fluid pressures and/or temperatures inside pipe cemented in well bores during testing, perforating, fluid injection and/or fluid production. The high internal pipe pressure and/or temperature results in expansion of the pipe, both radially and longitudinally, which places stresses on the cement sheath causing it to crack or the bonds between the exterior surfaces of the pipe and/or the well bore walls and the cement sheath to fail in the form of loss of hydraulic seal.
Another condition results from exceedingly high pressures which occur inside the cement sheath due to the thermal expansion of fluids trapped within the cement sheath. This condition often occurs as a result of high temperature differentials created during the injection or production of high temperature fluids through the well bore, e.g., wells subjected to steam recovery or the production of hot formation fluids from high temperature formations. Typically, the pressure of the trapped fluids exceeds the collapse pressure of the cement and pipe causing leaks and bond failure.
In multi-lateral wells wherein liners have been cemented in well bores using conventional well cement slurries which set into brittle solid masses, the brittle set cement often cannot withstand impacts and shocks subsequently generated by drilling and other well operations carried out in the laterals without cracking or shattering.
In wells which are completed in oil containing reservoirs whereby the casing is rigidly cemented in the well bore, one or more rock formations above the reservoir often subside as the oil is produced which causes movement of the rock formations transversely to the well bore. Because the set cement surrounding the casing is rigid and inflexible, the movement of the rock formations often relatively quickly causes the casing to be severed or crushed.
The cement compositions utilized in primary cementing must often be lightweight to prevent excessive hydrostatic pressures from being exerted on formations penetrated by well bores. In some applications, the heretofore utilized lightweight cement compositions have had densities such that the cement compositions can not be displaced into well annuluses all the way to the surface due to the hydrostatic pressure of the cement compositions exceeding the fracture gradient of one or more formations penetrated by the wells. The resulting upper unsupported portion of the casing can and often does experience early damage due to formation cave-ins, subsidence and the like.
Thus, there are needs for improved well completion and remedial compositions and methods which unlike conventional hydraulic cement compositions form highly pliable impermeable masses which can withstand the above described stresses without failure.